seems like there is a great diversity of uppers for the AR-15
many to change caliber
many to change configureation
i have seen uppers to shoot 50 BMG...and its not even considered a gun
lately seem a cross bow
NEVER SEEN A MUZZLE LOADER.
is it i just haven't seem one YET
what else have you seen?
what have you got?
what have you imagined or would like to see?